1. Technical Field
The present disclosure relates to plug-in hybrid electric vehicles (PHEVs) and electric vehicles (EVs) and more particularly to on-board chargers for such vehicles.
2. Description of Related Art
Plug-in hybrid electric vehicles (PHEVs) and electric vehicles (EVs), cumulatively called plug-in electric vehicles (PEVs), need to be equipped with an on-board charger. Such on-board chargers are generally categorized as onboard level-1 (L1) grid-to-vehicle (G2V) chargers and level-2 (L2) grid-to-vehicle (G2V) chargers to charge the high-voltage (HV) traction batteries in plug-in electric vehicles (PEVs).
FIGS. 1 and 2 illustrate schematic diagrams of an onboard power electronic interface (PEI) 102 of a PEV powertrain in presence of an onboard charger and a step-down dc-dc converter according to the prior art. More particularly, FIGS. 1 and 2 illustrate power electronic interface (PEI) 102 that includes a typical on-board charger 106 that is mounted on a PEV 100 according to the prior art. On-board charger 106 is supplied 1-phase alternating current (AC) electrical power by an external power supply interface connection 104. The on-board charger 106 includes two stages: (a) first stage 1060 is an AC/DC (direct current) converter for rectification and power factor correction; (b) second stage 1068 is an isolated DC/DC converter for galvanic isolation and battery current/voltage regulation[2-5]. Second stage DC/DC converter 1068 is in electrical communication with HV traction batteries 108.
The HV traction batteries 108 are in electrical communication with a low voltage (LV) system 110 that includes a step-down dc-dc converter 112 in electrical communication with LV batteries 114 and that steps down the voltage of HV traction batteries 108 to a typical 12-V low voltage (LV) to the level of LV batteries 114.
As defined herein, HV traction batteries 108 may include a single battery or multiple batteries. Similarly, LV batteries 114 may include a single battery or multiple batteries. HV fraction batteries 108 and LV batteries 114 may also be referred to herein as battery packs, even if there is only a single battery present.
to energize dc electrical loads, such as steering system, air conditioning, radios and consumer electronics. Such step-down dc-dc converter 112 is independent of the grid-connected onboard charger 106.
The most commonly used ac-dc converter 1064 includes a single-phase power factor correction (PFC) boost converter, which converts the 110V˜240V single-phase ac voltages received at external power supply interface connection 104 to a regulated dc voltage (typically around 390V). At the second stage, isolated dc-dc converter 1068 is utilized to regulate the current/voltage (typically 250V˜420V) of HV batteries 108 and provide galvanic isolation. A majority of the commercially available and upcoming onboard L1 and L2 chargers are unidirectional.
The DC output of HV batteries 108 is supplied to a 3-phase inverter 116 that is in electrical communication with a 3-phase motor 118 to form an electric propulsion system 1160. The 3-phase motor 118 is mechanically coupled to torque converter 120 and in turn transmission 122 and axle and wheel assembly 124. Internal combustion engine (ICE) propulsion system 126 is also mechanically coupled in parallel to the torque converter 120 and in turn transmission 122 and axle and wheel assembly 124.
In the case of availability of other renewable energy sources such as wind, solar, or fuel cell energy systems, the output of the energy source are sometimes directly connected to DC-link 1066, which is the stage between AC/DC stage 1064 and DC/DC stage 1068 and shown by VDC, enabling DC charging from the renewable energy source.
An efficient approach toward topology integration can increase the power density and specific power while reducing the cost of onboard PEIs. Prior efforts to develop integrated PEV onboard chargers include integration of non-isolated single-stage chargers that combine an ac-dc PFC converter and a dc-dc bidirectional converter, which interfaces an HV battery pack and the propulsion inverter. However, such topologies require more transistors and diodes, and integrating a high-power dc-dc converter with a low-power onboard charger might reduce the charging efficiency. In addition, some PEVs might not be equipped with a bidirectional converter between HV battery pack and propulsion inverter.
Other researchers have studied the integration of isolated onboard chargers using either phase-shift active-bridge converters or series-parallel resonant converters; however, many of these topologies require more components and have lower efficiency in comparison to stand-alone converters. Moreover, these topologies include a discrete inductor as the resonant inductor in series with the transformer, which increases the size and weight of magnetic components. Some topologies do not provide isolation between the HV traction battery and LV dc loads, which does not comply with the requirements of IEC 61851-1 Standard.
As described herein throughout the drawings and specification, the sequential numbering of the various components, such as switches S1, S2 . . . , diodes D1, D2 . . . , capacitors C1, C2 . . . , etc. are unique to the particular figure that is being described, and are not necessarily considered to carry over from one figure to the next unless the particular components are located on one or more other figures such that one of ordinary skill in the art would recognize that the component(s) in question is (are) in fact carried over from one or more previously described figures.
FIG. 3 demonstrates the topology of a typical onboard charger 106 and an individual dc-dc converter 110 according to the prior art. The first stage 1060 of charger 106 includes a unidirectional diode bridge 1051 for ac-dc conversion, followed by an interleaved boost converter 1052 (inductors L1 and L2, diodes D1 and D2, switches S1 and S2 and capacitor CDC1) for power factor correction. The first stage 1060 is in electrical communication with unidirectional LLC resonant converter 1068 (switches S3, S4, S5, S6, resonant inductor Lr1, resonant capacitor Cr1, transformer T1, diodes D3, D4, D5, D6 and capacitor Cdc2) that forms the second stage 1068 to regulate the voltage/current of the HV traction battery 108.
Via HV battery 108, the second stage 1068 is in electrical communication with LV system 110 that includes another LLC resonant converter 112 (switches S7, S8, S9, S10, resonant inductor Lr2, resonant capacitor Cr2, transformer T2, diodes D7, D8, D9, D10, switches S15, S16 and capacitor Cdc2) that delivers power from HV traction battery pack 108 to LV battery pack 114 that is electrically coupled to LV dc loads (not shown).